Abstract

For work on my thesis dissertation, we have been studying some energetic processes in solar flares. On our work on hard X-ray (HXR) emission from flares, we have shown that non-thermal recombination emission can compare with thebremsstrahlung HXR flux for certain flare conditions. In this thesis, we show spectral features characteristic of non-thermal recombination HXR emission and suggest how itplays a signicant role in the flare HXR continuum, something that has been ignored in the past. It is important to note that these results could demand a reconsideration of the numbers of accelerated electrons since recombination can be much more efficient inproducing HXR photons than bremsstrahlung. We go on to show that although nonthermal recombination is not likely to dominate the total HXR flux unless we considerextreme parameter regimes, it can still form a signicant proportion of the HXR flux for typical flare conditions, thereby remaining important for both spectral inversionand low energy electron cut-off diagnostic capabilities.

In related work on diagnosing particle acceleration in flares, we also have an interest in studying solar neutrons. To this end, this thesis presents our work done with new-age neutron detectors developed by our colleagues at the University of New Hampshire. Using laboratory and simulated data from the detector to produce its response matrix, we then employ regularisation and deconvolution techniques to produce encouraging results for data inversion. As a corollary, we have been reconsidering the role of inverse Compton scattering (ICS) of photospheric photons. Gamma-ray observations clearly show the presence of 100 MeV electrons and positrons in the solar corona, by-products of GeV energy ions. We present results of ICS of solar flare photons taking proper account of radiation field geometry near the solar surface. If observed, such radiation would let us determine the number of secondary positrons produced in large flares, contributing to a full picture of ion acceleration and to predictingneutron fluxes to be encountered by future inner heliosphere space missions.